This invention pertains to processes for producing n-butyl acrylate by the esterification of acrylic acid with n-butanol and to processes for refining butyl acrylate. In accordance with this invention, a splitter distillation column is used to make a separation between (i) lights, which include dibutyl ether, butyl acetate, butanol and lower boiling components and (ii) acrylate and heavies.
Butyl acrylate is prepared by the equilibrium-limited reaction of acrylic acid-and n-butanol. The reaction is conducted at elevated temperature in the presence of a catalyst. Typically, the coproduct, water, is removed during the course of the reaction to drive the reaction more toward the butyl acrylate product. In conducting this reaction, impurities in the raw materials and side reactions generate by-products that must be removed from the butyl acrylate.
Conventionally, the refining of the butyl acrylate-containing reaction product is conducted by distillation. The purification is generally done in several distillation column sections. U.S. Pat. No. 4,012,439 discloses a process for producing n-butyl acrylate free from dibutyl ether. In the disclosed process, the esterification reaction product is sent to a first distillation column. A ternary mixture containing butyl acrylate, butanol and water is the distillate. This distillate is condensed and subjected to phase separation, and the organic phase is delivered to a second distillation column from which a ternary distillate of butyl acrylate, butanol and water is obtained. The base product from this second distillation column contains butanol and butyl acrylate and is passed to a third distillation column for the separation of butanol from butyl acrylate.
U.S. Pat. No. 4,280,010 discloses a process for making butyl acrylate in which the reaction overhead is passed to a reactor column with the distillate being a butyl acrylate, butanol and water azeotrope. A reflux is used in the reactor column. The remainder of the distillate is sent to a dehydration column and the organic product is further distilled to provide a butanolxe2x80x94butyl acrylate azeotrope being recycled to the reactor and butyl acrylate stream being obtained at the base of the column.
U.S. Pat. No. 4,814,493 discloses another technique for making butyl acrylate. The reaction overhead is passed to a finishing distillation column. The finishing distillation column provides a side stream of butyl acrylate product, a bottoms stream that is recycled to the reactor and an overhead stream that is passed to a butanol recovery distillation column. The distillate from the butanol recovery column is recycled to the reactor. This patent also describes the use of a heat treater which receives a portion of the liquid from the reactor. The heat treater apparently cracks components which can then be separated from heavies via distillation column and returned to the reactor.
Butyl acrylate having high purity is sought. The process for making butyl acrylate, and the sources of raw materials for those processes, result in troublesome separations. One impurity is dibutyl ether which has a normal boiling point within 5xc2x0 to 7xc2x0 C. of that of butyl acrylate. This impurity can impart odor to the butyl acrylate. Another impurity is butyl acetate which is the esterification product of acetic acid, an impurity in acrylic acid, and butyl acetate can also impart odor to butyl acrylate.
Processes for manufacturing and refining butyl acrylate are sought which are economical, energy efficient and capable of providing butyl acrylate of enhanced purity. Moreover, processes are sought that enable the use of acrylic acid containing acetic acid and reaction conditions which enable dibutyl ether to be formed, yet provide a butyl acrylate product to be obtained of unexpectedly high purity.
In accordance with the processes of this invention, a fluid stream containing butyl acrylate, dibutyl ether, butyl acetate, and n-butanol is separated in a splitter distillation column to provide an overhead fraction containing dibutyl ether, butyl acetate and butanol and a bottoms fraction containing butyl acrylate and heavies. The overhead fraction typically contains butyl acrylate in addition to dibutyl ether, butyl acetate and butanol. The bottoms fraction preferably contains less than about 0.2 weight percent of total dibutyl ether and butyl acetate and less than about 10 percent of the total dibutyl ether and butyl acetate in the fluid stream. The overhead fraction from the splitter column is subjected to further distillation in the presence of water in a butanol recovery column to separate butanol and butyl acrylate from lights containing dibutyl ether and butyl acetate. The bottoms fraction from the splitter distillation column, comprising heavies and butyl acrylate, can advantageously be rectified in a butyl acrylate distillation column to separate heavies from the butyl acrylate.
In the aspect of the invention relating to esterification processes, n-butanol and acrylic acid are subjected, in at least one reaction zone, to esterification reaction conditions including the presence of an esterification catalyst, to produce butyl acrylate and water as well as side products including butyl acetate, heavies and dibutyl ether. A gaseous stream containing water, butanol, acrylic acid, butyl acrylate, butyl acetate, dibutyl ether and heavies is withdrawn from the reaction zone and passed to a reactor distillation column. The overhead from the reactor distillation column contains water, butanol, butyl acrylate, butyl acetate, dibutyl ether and heavies, and this overhead is condensed and subjected to liquid phase separation to remove most of the water, and the resulting organic phase is the liquid feed stream to the splitter distillation column as described above. The bottoms fraction from the reaction distillation column is rich in acrylic acid, at least a portion of which is recycled to at least one reaction zone.
The bottoms fraction from the splitter distillation column is advantageously rectified in a distillation column to separate heavies from the butyl acrylate. Recovered butyl acrylate has a purity of at least about 99.0 weight percent butyl acrylate, less than about 1000, more preferably less than about 200, and most preferably less than about 60, parts per million by weight (ppmw) dibutyl ether and preferably less than about 500, more preferably less than about 50, ppmw butyl acetate, with the sum of dibutyl ether, and butyl acetate preferably being less than about 1500 ppm. More preferably, the recovered butyl acrylate has a purity of at least about 99.5, more preferably at least about 99.8, and most preferably 99.9, weight percent butyl acrylate and less than about 400, and most preferably less than about 300, ppmw of total dibutyl ether and butyl acetate. At least a portion of the recovered heavies can be recycled to at least one esterification reaction zone or supplied to another reaction zone to crack the heavies and regenerate butanol and acrylic acid.